1. Field of the Invention
The present invention relates to a data communication apparatus for transmitting a color image.
2. Description of the Prior Art
A facsimile machine is used widely for transmitting an image, and a facsimile communication of a color image is already realized. Usually, a facsimile machine of the reception side prints out a received image promptly. This immediacy enhances the value of the facsimile communication.
There is another transmission form such as E-mail communication in a LAN or the Internet. A receiver can open E-mail at any time, and an image that was received as an attached file can be displayed on a screen or can be printed out. The E-mail communication is useful when concealment and reliability are important.
Conventionally, a communication apparatus is proposed in which the facsimile communication and the E-mail communication are used selectively automatically. Japanese unexamined patent publication No. 11-69126 discloses a communication apparatus that memorizes registration information that indicates whether the image transmission by the E-mail communication is permitted or not for each party and transmits the image by the facsimile communication to the party to which the image transmission by E-mail communication is not permitted while sending a notify of the image transmission by E-mail to the party.
In data communication of a color image, there are some problems. If the color reproduction range of the image output in the reception side is narrower than the color range of the transmission data (the original image), some of colors may be outputted in different colors, or a color balance of the entire image may be lost. Especially, this problem is serious in the communication whose main purpose is to transmit color information (for example, a response to a question about a color of merchandise).
Since the reproduction range of the print is usually narrower than that of the color screen display, a conspicuous color shift can be generated easily between the original image and the print image when printing out in the reception side. There is a countermeasure for the problem of the color balance, i.e., a color compression process can be used for narrowing the color range of the original image to the color reproduction range. However, even if the color compression is performed, the color of the original image cannot be reproduced faithfully. In order to reproduce the color of the original image faithfully, the original image may be transmitted as an attached file of E-mail to the party. However, because of a familiar usage or a high immediacy, there is a tendency to prefer the facsimile transmission for transmitting image data. Conventionally, the facsimile communication cannot improve the above-mentioned color shift. If a user has to set a transmission form at every transmission, it causes a bad usability as well as losing the immediacy as the E-mail transmission is used when the facsimile communication can be used without any problem.